In an integrated circuit, a silicon dioxide film (SiO2 film) by the plasma CVD (chemical vapor deposition) method has so far been used as an interlayer dielectric film. However, because of high integration of transistors and speeding of a switching action, losses due to capacitance between wirings have posed problems. To eliminate these losses, it is necessary to decrease the relative dielectric constant of the interlayer dielectric film, so that an interlayer dielectric film with a lower relative dielectric constant has been demanded. Under these circumstances, films of organic materials (for example, organosilicon films or films of amorphous carbon incorporating fluorine) can be provided with a very low relative dielectric constant (relative dielectric constant κ=2.5 or less), but these films have been problematical in mechanical and chemical resistance and thermal conductivity. Adhesion of the films has also presented a problem, and their moisture absorption resistance has been a problem in terms of density.
Under these circumstances, boron nitride (BN) and boron carbonitride (BNC), which are excellent in heat resistance and have a very low relative dielectric constant (relative dielectric constant κ=2.5 or less), are attracting attention. However, techniques for forming a BN film or a BNC film by the plasma CVD (chemical vapor deposition) method have not been established, and the advent of a film forming method and a film forming apparatus capable of forming a BN film and a BNC film as products is in eager demand.
The present invention has been accomplished in view of the above situations, and its object is to provide a film forming method and a film forming apparatus which can form films of boron nitride and boron carbonitride.